Malfunction of apparatus, and particularly in vehicles, for example malfunction within an engine or operating control system of an automotive vehicle, is frequently indicated by a warning lamp. Such a warning lamp may, for example, be used to indicate a simple malfunction. Such warning lamps can be controlled in a different manner, for example by lighting as soon as a malfunction is detected or, if the malfunction is serious, intermittently flashing. Thus, a single warning lamp may provide differential output to characterize two different conditions.
Continuous illumination may be used to indicate a simple malfunction. This requires a continuous control signal, for example a "high voltage level" at a connecting line to a warning lamp. If the lamp flashes, however, a malfunction of a specific type may be indicated thereby.
It would, of course, be possible to associate individual warning lamps with different causes for malfunction. It is, however, equally possible to provide a single warning lamp which may be either continuously illuminated or be intermittently illuminated, that is, to flash, and in addition to provide a display on which the type of malfunction is displayed. The warning lamp, thus, alerts the operator to read the display. The display itself may be coupled to a diagnostic apparatus for precise indication, by alphanumeric or symbolic representation, of the particular type of malfunction of message to be conveyed to the operator.
Controlling a diagnostic display apparatus, heretofore, has required a plurality of connecting lines. Furthermore, the warning lamp requires a connecting line. The additional connecting lines and the plurality of wires are, again, subject to malfunction, require additional material and installation and, further, require separate outputs to the respective warning lamps or display elements. Commercial circuit arrangements for monitoring or testing of apparatus elements or continuous operating sequences carried out by machinery frequently have only few output terminals. Providing additional diagnostic apparatus to be coupled to the few output terminals makes the circuit requirements for the test and monitoring circuit complex and expensive. Entirely apart from the expense, the increased complexity again may be a source of malfunction.